Displaying a Dialog Window

Displaying a Dialog Window

There are times where you need to display a dialog window to get a confirmation from the user. In this case, you can override the onCreateDialog() protected method defined in the base Activity  class to display a dialog window. The following Try It Out shows you how.

1. Using Eclipse, create a new Android project and name it Dialog.
2. Add the following statements in bold to the main.xml file:
 

<?xml version=”1.0” encoding=”utf-8”?>
      <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android”
             android:orientation=”vertical”
             android:layout_width=”fill_parent”
             android:layout_height=”fill_parent” >
     <TextView
            android:layout_width=”fill_parent”
            android:layout_height=”wrap_content”
            android:text=”@string/hello” />
     <Button
            android:id=”@+id/btn_dialog”
            android:layout_width=”fill_parent”
           android:layout_height=”wrap_content”
           android:text=”Click to display a dialog” />
     </LinearLayout>

3. Add the following statements in bold to the MainActivity.java file:

        package net.learn2develop.Dialog;
            import android.app.Activity;
            import android.os.Bundle;
            import android.app.AlertDialog;
            import android.app.Dialog;
            import android.content.DialogInterface;
            import android.view.View;
            import android.widget.Button;
            import android.widget.Toast;
      public class MainActivity extends Activity

      {
             CharSequence[] items = { “Google”, “Apple”, “Microsoft” };
             boolean[] itemsChecked = new boolean [items.length];
            /** Called when the activity is first created. */
             @Override
      public void onCreate(Bundle savedInstanceState) 

      {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);
            Button btn = (Button) findViewById(R.id.btn_dialog);
        btn.setOnClickListener(new View.OnClickListener()

        {
          public void onClick(View v) 

          {
               showDialog(0);
          }
     });
}
  @Override
    protected Dialog onCreateDialog(int id) 

    {
       switch (id) {
        case 0: return new AlertDialog.Builder(this)
        .setIcon(R.drawable.icon)
        .setTitle(“This is a dialog with some simple text...”)
        .setPositiveButton(“OK”, new
    DialogInterface.OnClickListener() 

    {
       public void onClick(DialogInterface dialog, int whichButton)
       {
            Toast.makeText(getBaseContext(),
            “OK clicked!”, Toast.LENGTH_SHORT).show();
       }
 })
         .setNegativeButton(“Cancel”, new
         DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton)
  {
          Toast.makeText(getBaseContext(),
           “Cancel clicked!”, Toast.LENGTH_SHORT).show();
   }
})

    .setMultiChoiceItems(items, itemsChecked, new
     DialogInterface.OnMultiChoiceClickListener() {
     @Override
   public void onClick(DialogInterface dialog, int which, boolean isChecked) 

    {
       Toast.makeText(getBaseContext(),
        items[which] + (isChecked ? “ checked!”: “ unchecked!”),
        Toast.LENGTH_SHORT).show();
    }
  }
) .create();
} return null;
  }
}

4. Press F11 to debug the application on the Android Emulator. Click the button to display the dialog (see Figure). Checking the various checkboxes will cause the Toast class to display the text of the item checked/unchecked. To dismiss the dialog, click the OK or Cancel button.

How It Works

  To display a dialog, you first override the onCreateDialog() method in the Activity class:
      @Override
       protected Dialog onCreateDialog(int id) 

       {
        //... some code
       }

This method is called when you call the showDialog() method:

  Button btn = (Button) findViewById(R.id.btn_dialog);
  btn.setOnClickListener(new View.OnClickListener() 

  {
     public void onClick(View v) 

      {
          showDialog(0);
      }
});

The onCreateDialog() method is a callback for creating dialogs that are managed by the activity. When you call the showDialog() method, this callback will be invoked. The showDialog() method accepts an integer argument identifying a particular dialog to display.
To create a dialog, you use the AlertDialog class’s Builder constructor. You set the various properties, such as icon, title, and buttons, as well as checkboxes:

   @Override
   protected Dialog onCreateDialog(int id)

   {
        switch (id) {
        case 0: return new AlertDialog.Builder(this)
               .setIcon(R.drawable.icon)
               .setTitle(“This is a dialog with some simple text...”)
               .setPositiveButton(“OK”, new
      DialogInterface.OnClickListener() 

      {
          public void onClick(DialogInterface dialog, int whichButton)
          {
                  Toast.makeText(getBaseContext(),
                  “OK clicked!”, Toast.LENGTH_SHORT).show();
           }
})
                  .setNegativeButton(“Cancel”, new
         DialogInterface.OnClickListener()

         {
             public void onClick(DialogInterface dialog, int whichButton)
             {
                     Toast.makeText(getBaseContext(),
                     “Cancel clicked!”, Toast.LENGTH_SHORT).show();
              }
    })
                      .setMultiChoiceItems(items, itemsChecked, new
                       DialogInterface.OnMultiChoiceClickListener() 

                        {
           @Override
           public void onClick(DialogInterface dialog, int which, boolean isChecked)

           {
                 Toast.makeText(getBaseContext(),
                  items[which] + (isChecked ? “ checked!”: “ unchecked!”),
                  Toast.LENGTH_SHORT).show();
            }
        }
    ) .create();
  } return null;
}

The preceding code sets two buttons: OK and Cancel, using the setPositiveButton() and setNegativeButton() methods, respectively. You also set a list of checkboxes for users to choose via the setMultiChoiceItems() method. For the setMultiChoiceItems() method, you passed in two arrays: one for the list of items to display and another to contain the value of each item to indicate if they are checked. When each item is checked, you use the Toast class to
display a message (see Figure).